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Message-ID: <aBJa7qrdMcIEt7y8@google.com>
Date: Wed, 30 Apr 2025 10:16:30 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Thomas Richter <tmricht@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
linux-perf-users@...r.kernel.org, acme@...nel.org,
agordeev@...ux.ibm.com, gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
hca@...ux.ibm.com, irogers@...gle.com, ctshao@...gle.com
Subject: Re: [PATCH V4] perf test: Allow tolerance for leader sampling test
Hello,
On Wed, Apr 30, 2025 at 04:06:11PM +0200, Thomas Richter wrote:
> V4: Update to be applied onto linux-next
> V3: Added check for missing samples as suggested by Chun-Tse.
> V2: Changed bc invocation to return 0 on success and 1 on error.
>
> There is a known issue that the leader sampling is inconsistent, since
> throttle only affect leader, not the slave. The detail is in [1]. To
> maintain test coverage, this patch sets a tolerance rate of 80% to
> accommodate the throttled samples and prevent test failures due to
> throttling.
>
> [1] lore.kernel.org/20250328182752.769662-1-ctshao@...gle.com
>
> Signed-off-by: Chun-Tse Shao <ctshao@...gle.com>
> Suggested-by: Ian Rogers <irogers@...gle.com>
> Suggested-by: Thomas Richter <tmricht@...ux.ibm.com>
> Tested-by: Thomas Richter <tmricht@...ux.ibm.com>
> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
> ---
> tools/perf/tests/shell/record.sh | 33 ++++++++++++++++++++++++++------
> 1 file changed, 27 insertions(+), 6 deletions(-)
>
> diff --git a/tools/perf/tests/shell/record.sh b/tools/perf/tests/shell/record.sh
> index 05d91a663fda..587f62e34414 100755
> --- a/tools/perf/tests/shell/record.sh
> +++ b/tools/perf/tests/shell/record.sh
> @@ -240,22 +240,43 @@ test_leader_sampling() {
> err=1
> return
> fi
> + perf script -i "${perfdata}" | grep brstack > $script_output
> + # Check if the two instruction counts are equal in each record.
> + # However, the throttling code doesn't consider event grouping. During throttling, only the
> + # leader is stopped, causing the slave's counts significantly higher. To temporarily solve this,
> + # let's set the tolerance rate to 80%.
> + # TODO: Revert the code for tolerance once the throttling mechanism is fixed.
> index=0
> - perf script -i "${perfdata}" > "${script_output}"
> + valid_counts=0
> + invalid_counts=0
> + tolerance_rate=0.8
> while IFS= read -r line
> do
> - # Check if the two instruction counts are equal in each record
> cycles=$(echo $line | awk '{for(i=1;i<=NF;i++) if($i=="cycles:") print $(i-1)}')
> if [ $(($index%2)) -ne 0 ] && [ ${cycles}x != ${prev_cycles}x ]
> then
> - echo "Leader sampling [Failed inconsistent cycles count]"
> - err=1
> - return
> + invalid_counts=$(($invalid_counts+1))
> + else
> + valid_counts=$(($valid_counts+1))
> fi
> index=$(($index+1))
> prev_cycles=$cycles
> done < "${script_output}"
> - echo "Basic leader sampling test [Success]"
> + total_counts=$(bc <<< "$invalid_counts+$valid_counts")
> + if (( $(bc <<< "$total_counts <= 0") ))
> + then
> + echo "Leader sampling [No sample generated]"
> + err=1
> + return
> + fi
> + isok=$(bc <<< "scale=2; if (($invalid_counts/$total_counts) < (1-$tolerance_rate)) { 0 } else { 1 };")
I think the 'if-else' part can be omitted but I can live with that. :)
Thanks,
Namhyung
> + if [ $isok -eq 1 ]
> + then
> + echo "Leader sampling [Failed inconsistent cycles count]"
> + err=1
> + else
> + echo "Basic leader sampling test [Success]"
> + fi
> }
>
> test_topdown_leader_sampling() {
> --
> 2.45.2
>
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